Microcontinent Evolution of Isla Ángel de la Guarda, Gulf of California, México, from Neotectonic Mapping, Luminescence Dating, and Topographic Analysis
Abstract
The age, sense of slip, and orientation of faults on microcontinents can record the evolution of plate boundaries. However, most microcontinents are submarine and difficult to study at high-resolution. The Isla Ángel de la Guarda (IAG) microcontinent in the Gulf of California is a rare, subaerially exposed microcontinent of continental crust (30 x 100 km) within the active Pacific-North America plate boundary. We use high-resolution satellite- (3 m-resolution) and drone-based (~10 cm-resolution) imagery and topography and 13 luminescence ages to show that the southern part of IAG is the likely site of an incipient plate boundary reorganization that could lead to the breakup of the microcontinent. Our new mapping suggests that a N-S-striking normal fault system transects the southeastern part of IAG, and projects south offshore towards a ~NE-SW-trending spreading center in the North Salsipuedes Basin. New late Pleistocene and Holocene luminescence ages from faulted non-marine terrace deposits and sag pond deposits dammed against uphill-facing fault scarps indicate late Quaternary fault movement: after 52.0 ± 4.7 ka, after 37.6 ± 4.3 ka, between 11.7 ± 4.4 ka and 6.5 ± 1.4 ka, and before 9.4 ± 0.8 ka on different strands of the normal fault system. Historic seismicity within this N-S-striking fault system suggests ongoing, dextral, oblique-normal fault activity. We also extract channel profile gradients, networks, and plan view geometries in the mountains of southwestern IAG from our satellite topography to infer spatial and temporal patterns of tectonic activity. Collectively, these observations suggest that the North Salsipuedes Basin is kinematically linked with the active faults onshore of IAG and that crustal extension on southeastern IAG may connect to rift-related structures east of the island, where it could be in the process of reactivating an extinct plate boundary in the Upper Tiburón basin. A developing zone of active faulting in southern IAG would be consistent with the relatively young age of the North Salsipuedes Basin as a recently formed pull-apart basin along the Ballenas transform fault system. Such evolution of the Pacific-North America plate boundary may lead to the breakup and fragmentation of the IAG microcontinent if extension in the North Salsipuedes Basin and on southeastern IAG continues.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMEP035..06H
- Keywords:
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- 1125 Chemical and biological geochronology;
- GEOCHRONOLOGY;
- 1130 Geomorphological geochronology;
- GEOCHRONOLOGY;
- 1140 Thermochronology;
- GEOCHRONOLOGY;
- 1150 Cosmogenic-nuclide exposure dating;
- GEOCHRONOLOGY